I dont quite understand the question to be honest...
300+ Ah of battery capacity is HUGE!
Firstly will you have BOTH battery banks on board at the same time?
Any how wether adding capacity or adding a charger is the best option depends on the camping you are doing.
If you are camping predominantly for extended periods in one place with no power connections then adding capacity MAY be the better option. Other wise supplimenting a smaller bank (say 200Ah) with solar would be the better option.
If you are touring and moving camp every day or couple of days then 100Ah of capacity should be MORE than enough.
If you are camping at places which have access to 240V then 100Ah with a mains charger will be the best choice.
Picture this, you set up camp in a remote place no access to 240V power and you plan to stay 5 nights but you only have capacity for 3.
Well fistly if we move between 1/3 and 1/2 of that battery power to the vehicle which charges the batterys every time you go for a drive and connect this to the trailer when at camp via an anderson plug setup then we should see out 5 days without too much of a worry.
If we add a solar panel (roughly 80 - 100watts) to the trailer setup instead (remote solar would be my choice rather than fixed) then we also should see out the 5 days + with no worries and we dont have to drive the car.
If we add a combination of the two above mentioned methods then surely weeks of remote camping are possible.
I would be very interested to see what is sucking the juice though as that is a lot of RC to be going through in 3 days. That said i drain a 100Ah battery in roughly 30 hours just running the fridge. However I run a Waeco CF-80 which is a very large fridge and I run it on the coldest setting and I run it on "high" mode rather than "economy" mode so i can see how 330Ah could run down in 3 days